The present invention relates to gasoline fuel injection pumps for delivering high pressure fuel to a common rail.
Gasoline Direct Injection (GDI) fuel systems must regulate the fuel volume delivered to the common rail as part of an overall pressure management strategy. Two strategies are currently employed for controlling the quantity of fuel delivered to the pumping chamber and thus the degree to which the common rail is pressurized. One strategy uses a digital on/off solenoid such as disclosed in U.S. Pat. No. 7,707,996 and another uses a proportional valve such as disclosed in U.S. Pat. No. 6,792,916.
In cases where a proportional control valve is preferred there is a risk of diminished valve performance experienced as slowed response times and loss of functional stroke length due to the entrapment of fuel in the fluid chamber of the proportional control valve on the non-functional side of the metering piston. Fuel can become trapped in the inert volume of the valve by leakage through many potential paths, but is most likely to occur by leakage past the metering piston from the pump supply when pressure in the control valve rises in response to the operation of the pumping mechanism permitted by the finite response time of the inlet check valve. As fuel accumulates in the inert volume of the proportional control valve it will begin to retard the motion of the proportional control valve by requiring the valve to either pressurize that trapped fluid on pull-in or expel it through the same highly restricted leakage paths it entered through. This ultimately necessitates a solenoid and proportional valve system that produces more force on the piston and increases cost.